1. Field of the Invention
The present invention relates to a mine ventilation structure used to block a passageway or to prevent mixture of ventilation air at the intersection of two passageways. The ventilation structure blocking a passageway can be a shaft partition, stopping or regulator. The ventilation structure preventing the mixture of ventilation air at the intersection of two passageways can be an overcast or an undercast.
2. Brief Description of the Prior Art
In an underground mine having a grid of intersecting passageways separated by columns of remaining material, there is a need for a ventilation system as the mining activity becomes more distant from a source of ventilation. In a typical ventilation system, intake air and return air are ducted through air shafts formed by selected passageways. Along the air shafts, intersecting passageways are blocked with a partition or ducted through an overcast or an undercast.
The return air in a coal mine contains coal dust and methane so it is important that there be no intermingling of the return air with the intake air. Permanent barriers, such as those constructed of concrete block, steel plates or the like, have been used to define the passageways forming the air shafts. Even though the prior art structures are treated with sealants, a significant amount of air leaks through these structures, heard in the mine as a sucking sound. At overcasts and undercasts, the leaks result in intermingling of the return and intake air and at the barriers result in a significant loss of pressure when repeated at multiple barriers along shafts that may extend for thousands of feet.
In addition to leaking air, prior art partitions, overcasts and undercasts made of concrete blocks, steel plates and the like require large amounts of materials that are heavy and difficult to handle in the confined space within a mine. For example, an overcast made with sidewalls of concrete block takes about eight pallets of block, loaded two pallets to a trailer, plus five pallets of mortar. If the deck is suspended on iron beams, the beams weigh about 600 pounds and are lifted into place by hand because of space limitations. Concrete planks are laid over the beams, requiring several more pallets of materials. Bucket-type mine sealant is applied to the deck to seal the gaps between the planks and to seal the ends of the sidewalls to the coal columns between which they are installed. It takes a crew of six men about three shifts to construct an overcast, the work is dangerous and injuries are common. The space between the planks and the gap between the ends of the walls and the coal columns open up in time. Similar construction and leakage problems are encountered with overcasts made of steel plates that are bolted together.